Mercury treatment system in exhaust gas

Abstract

Disclosed is an Hg removal system which removes Hg contained in flue gas (12) from a boiler (11), in which the Hg removal system includes an ammonium chloride solution supply means (a reduction oxidation assistant supply means) (16) that sprays an NH 4 Cl solution (14), which contains ammonium chloride as a reduction oxidation assistant, into a flue gas duct (13) that is in the downstream of the boiler (11), a reduction denitration device (a reduction denitration means) (17) that contains a denitration catalyst which reduces NOx in the flue gas (12) with an NH 3 gas, while oxidizing metallic mercury (Hg 0 ) in the coexistence of an HCl gas, a heat exchanger (18) that performs heat exchange of the denitrated flue gas (12), a precipitator (19) that removes soot and dust in the denitrated flue gas (12), a wet desulfurization device (21) that removes divalent Hg 2+ , which is oxidized in the reduction denitration device (17), using a limestone and gypsum slurry (an alkali absorbent) (20), and a removal assistant supply means (23) that supplies a removal assistant (22) for removing impurities into the limestone and gypsum slurry (20) that circulates through the wet desulfurization device (21).

Description

technical field [0001] The present invention relates to a treatment system capable of removing mercury in exhaust gas to a low concentration of mercury in exhaust gas. Background technique [0002] In the exhaust gas generated when coal combustion exhaust gas or heavy oil is burned, in addition to smoke, sulfur oxides (SOx), nitrogen oxides (NOx), sometimes metal mercury (Hg 0 ). In recent years, metal mercury (Hg 0 ) methods and devices have been investigated. [0003] As a treatment for metallic mercury (Hg) in exhaust gas 0 ) method, it is proposed that the NH 4 A method of spraying a Cl solution in a liquid state and supplying it into a flue (for example, refer to Patent Documents 1 and 2). Will NH 4 When the Cl solution is sprayed into the flue in a liquid state, the NH 4 Cl dissociates to form ammonia (NH 3 ) gas, hydrogen chloride (HCl) gas. NH 3 The gas functions as a reducing agent, and the HCl gas functions as a mercury chlorination agent (oxidation aid)....

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Problems solved by technology

[0017] However, as shown in the proposal of Patent Document 3, there is a problem that even if the peroxidation state of the absorption tower is removed, the oxides such as dithionate, peroxodisulfate, etc. that have been generated in the peroxidation state cannot be oxidized. Object (S 2 o 6 2- , S 2 o 8 2- ), hexavalent selenium (Se 6+ ) and so on to remove

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